signal.c

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/*
 * OpenRISC signal.c
 *
 * Linux architectural port borrowing liberally from similar works of
 * others.  All original copyrights apply as per the original source
 * declaration.
 *
 * Modifications for the OpenRISC architecture:
 * Copyright (C) 2003 Matjaz Breskvar <[email protected]>
 * Copyright (C) 2010-2011 Jonas Bonn <[email protected]>
 *
 *      This program is free software; you can redistribute it and/or
 *      modify it under the terms of the GNU General Public License
 *      as published by the Free Software Foundation; either version
 *      2 of the License, or (at your option) any later version.
 */

#include <linux/sched.h>
#include <linux/mm.h>
#include <linux/smp.h>
#include <linux/kernel.h>
#include <linux/signal.h>
#include <linux/errno.h>
#include <linux/wait.h>
#include <linux/ptrace.h>
#include <linux/unistd.h>
#include <linux/stddef.h>
#include <linux/tracehook.h>

#include <asm/processor.h>
#include <asm/ucontext.h>
#include <asm/uaccess.h>

#define DEBUG_SIG 0

asmlinkage long
_sys_sigaltstack(const stack_t *uss, stack_t *uoss, struct pt_regs *regs)
{
    return do_sigaltstack(uss, uoss, regs->sp);
}

struct rt_sigframe {
    struct siginfo *pinfo;
    void *puc;
    struct siginfo info;
    struct ucontext uc;
    unsigned char retcode[16];  /* trampoline code */
};

static int restore_sigcontext(struct pt_regs *regs, struct sigcontext *sc)
{
    unsigned int err = 0;

    /* Alwys make any pending restarted system call return -EINTR */
    current_thread_info()->restart_block.fn = do_no_restart_syscall;

    /*
     * Restore the regs from &sc->regs.
     * (sc is already checked for VERIFY_READ since the sigframe was
     *  checked in sys_sigreturn previously)
     */
    if (__copy_from_user(regs, sc->regs.gpr, 32 * sizeof(unsigned long)))
        goto badframe;
    if (__copy_from_user(&regs->pc, &sc->regs.pc, sizeof(unsigned long)))
        goto badframe;
    if (__copy_from_user(&regs->sr, &sc->regs.sr, sizeof(unsigned long)))
        goto badframe;

    /* make sure the SM-bit is cleared so user-mode cannot fool us */
    regs->sr &= ~SPR_SR_SM;

    /* TODO: the other ports use regs->orig_XX to disable syscall checks
     * after this completes, but we don't use that mechanism. maybe we can
     * use it now ?
     */

    return err;

badframe:
    return 1;
}

asmlinkage long _sys_rt_sigreturn(struct pt_regs *regs)
{
    struct rt_sigframe *frame = (struct rt_sigframe __user *)regs->sp;
    sigset_t set;

    /*
     * Since we stacked the signal on a dword boundary,
     * then frame should be dword aligned here.  If it's
     * not, then the user is trying to mess with us.
     */
    if (((long)frame) & 3)
        goto badframe;

    if (!access_ok(VERIFY_READ, frame, sizeof(*frame)))
        goto badframe;
    if (__copy_from_user(&set, &frame->uc.uc_sigmask, sizeof(set)))
        goto badframe;

    set_current_blocked(&set);

    if (restore_sigcontext(regs, &frame->uc.uc_mcontext))
        goto badframe;

    /* It is more difficult to avoid calling this function than to
       call it and ignore errors.  */
    if (do_sigaltstack(&frame->uc.uc_stack, NULL, regs->sp) == -EFAULT)
        goto badframe;

    return regs->gpr[11];

badframe:
    force_sig(SIGSEGV, current);
    return 0;
}

/*
 * Set up a signal frame.
 */

static int setup_sigcontext(struct sigcontext *sc, struct pt_regs *regs,
                unsigned long mask)
{
    int err = 0;

    /* copy the regs */

    err |= __copy_to_user(sc->regs.gpr, regs, 32 * sizeof(unsigned long));
    err |= __copy_to_user(&sc->regs.pc, &regs->pc, sizeof(unsigned long));
    err |= __copy_to_user(&sc->regs.sr, &regs->sr, sizeof(unsigned long));

    /* then some other stuff */

    err |= __put_user(mask, &sc->oldmask);

    return err;
}

static inline unsigned long align_sigframe(unsigned long sp)
{
    return sp & ~3UL;
}

/*
 * Work out where the signal frame should go.  It's either on the user stack
 * or the alternate stack.
 */

static inline void __user *get_sigframe(struct k_sigaction *ka,
                    struct pt_regs *regs, size_t frame_size)
{
    unsigned long sp = regs->sp;
    int onsigstack = on_sig_stack(sp);

    /* redzone */
    sp -= STACK_FRAME_OVERHEAD;

    /* This is the X/Open sanctioned signal stack switching.  */
    if ((ka->sa.sa_flags & SA_ONSTACK) && !onsigstack) {
        if (current->sas_ss_size)
            sp = current->sas_ss_sp + current->sas_ss_size;
    }

    sp = align_sigframe(sp - frame_size);

    /*
     * If we are on the alternate signal stack and would overflow it, don't.
     * Return an always-bogus address instead so we will die with SIGSEGV.
     */
    if (onsigstack && !likely(on_sig_stack(sp)))
        return (void __user *)-1L;

    return (void __user *)sp;
}

/* grab and setup a signal frame.
 *
 * basically we stack a lot of state info, and arrange for the
 * user-mode program to return to the kernel using either a
 * trampoline which performs the syscall sigreturn, or a provided
 * user-mode trampoline.
 */
static int setup_rt_frame(int sig, struct k_sigaction *ka, siginfo_t *info,
              sigset_t *set, struct pt_regs *regs)
{
    struct rt_sigframe *frame;
    unsigned long return_ip;
    int err = 0;

    frame = get_sigframe(ka, regs, sizeof(*frame));

    if (!access_ok(VERIFY_WRITE, frame, sizeof(*frame)))
        goto give_sigsegv;

    err |= __put_user(&frame->info, &frame->pinfo);
    err |= __put_user(&frame->uc, &frame->puc);

    if (ka->sa.sa_flags & SA_SIGINFO)
        err |= copy_siginfo_to_user(&frame->info, info);
    if (err)
        goto give_sigsegv;

    /* Clear all the bits of the ucontext we don't use.  */
    err |= __clear_user(&frame->uc, offsetof(struct ucontext, uc_mcontext));
    err |= __put_user(0, &frame->uc.uc_flags);
    err |= __put_user(NULL, &frame->uc.uc_link);
    err |= __put_user((void *)current->sas_ss_sp,
              &frame->uc.uc_stack.ss_sp);
    err |= __put_user(sas_ss_flags(regs->sp), &frame->uc.uc_stack.ss_flags);
    err |= __put_user(current->sas_ss_size, &frame->uc.uc_stack.ss_size);
    err |= setup_sigcontext(&frame->uc.uc_mcontext, regs, set->sig[0]);

    err |= __copy_to_user(&frame->uc.uc_sigmask, set, sizeof(*set));

    if (err)
        goto give_sigsegv;

    /* trampoline - the desired return ip is the retcode itself */
    return_ip = (unsigned long)&frame->retcode;
    /* This is l.ori r11,r0,__NR_sigreturn, l.sys 1 */
    err |= __put_user(0xa960, (short *)(frame->retcode + 0));
    err |= __put_user(__NR_rt_sigreturn, (short *)(frame->retcode + 2));
    err |= __put_user(0x20000001, (unsigned long *)(frame->retcode + 4));
    err |= __put_user(0x15000000, (unsigned long *)(frame->retcode + 8));

    if (err)
        goto give_sigsegv;

    /* TODO what is the current->exec_domain stuff and invmap ? */

    /* Set up registers for signal handler */
    regs->pc = (unsigned long)ka->sa.sa_handler; /* what we enter NOW */
    regs->gpr[9] = (unsigned long)return_ip;     /* what we enter LATER */
    regs->gpr[3] = (unsigned long)sig;           /* arg 1: signo */
    regs->gpr[4] = (unsigned long)&frame->info;  /* arg 2: (siginfo_t*) */
    regs->gpr[5] = (unsigned long)&frame->uc;    /* arg 3: ucontext */

    /* actually move the usp to reflect the stacked frame */
    regs->sp = (unsigned long)frame;

    return 0;

give_sigsegv:
    force_sigsegv(sig, current);
    return -EFAULT;
}

static inline void
handle_signal(unsigned long sig,
          siginfo_t *info, struct k_sigaction *ka,
          struct pt_regs *regs)
{
    int ret;

    ret = setup_rt_frame(sig, ka, info, sigmask_to_save(), regs);
    if (ret)
        return;

    signal_delivered(sig, info, ka, regs,
                 test_thread_flag(TIF_SINGLESTEP));
}

/*
 * Note that 'init' is a special process: it doesn't get signals it doesn't
 * want to handle. Thus you cannot kill init even with a SIGKILL even by
 * mistake.
 *
 * Also note that the regs structure given here as an argument, is the latest
 * pushed pt_regs. It may or may not be the same as the first pushed registers
 * when the initial usermode->kernelmode transition took place. Therefore
 * we can use user_mode(regs) to see if we came directly from kernel or user
 * mode below.
 */

void do_signal(struct pt_regs *regs)
{
    siginfo_t info;
    int signr;
    struct k_sigaction ka;

    /*
     * We want the common case to go fast, which
     * is why we may in certain cases get here from
     * kernel mode. Just return without doing anything
     * if so.
     */
    if (!user_mode(regs))
        return;

    signr = get_signal_to_deliver(&info, &ka, regs, NULL);

    /* If we are coming out of a syscall then we need
     * to check if the syscall was interrupted and wants to be
     * restarted after handling the signal.  If so, the original
     * syscall number is put back into r11 and the PC rewound to
     * point at the l.sys instruction that resulted in the
     * original syscall.  Syscall results other than the four
     * below mean that the syscall executed to completion and no
     * restart is necessary.
     */
    if (regs->orig_gpr11) {
        int restart = 0;

        switch (regs->gpr[11]) {
        case -ERESTART_RESTARTBLOCK:
        case -ERESTARTNOHAND:
            /* Restart if there is no signal handler */
            restart = (signr <= 0);
            break;
        case -ERESTARTSYS:
            /* Restart if there no signal handler or
             * SA_RESTART flag is set */
            restart = (signr <= 0 || (ka.sa.sa_flags & SA_RESTART));
            break;
        case -ERESTARTNOINTR:
            /* Always restart */
            restart = 1;
            break;
        }

        if (restart) {
            if (regs->gpr[11] == -ERESTART_RESTARTBLOCK)
                regs->gpr[11] = __NR_restart_syscall;
            else
                regs->gpr[11] = regs->orig_gpr11;
            regs->pc -= 4;
        } else {
            regs->gpr[11] = -EINTR;
        }
    }

    if (signr <= 0) {
        /* no signal to deliver so we just put the saved sigmask
         * back */
        restore_saved_sigmask();
    } else {        /* signr > 0 */
        /* Whee!  Actually deliver the signal.  */
        handle_signal(signr, &info, &ka, regs);
    }

    return;
}

asmlinkage void do_notify_resume(struct pt_regs *regs)
{
    if (current_thread_info()->flags & _TIF_SIGPENDING)
        do_signal(regs);

    if (current_thread_info()->flags & _TIF_NOTIFY_RESUME) {
        clear_thread_flag(TIF_NOTIFY_RESUME);
        tracehook_notify_resume(regs);
    }
}